<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <div id="test-div">文本</div>
    <style>
        .div {
            background-color: red;
            font-size: 30px;
        }
    </style>
    <script>
        const el = document.getElementById("test-div");
        el.style.backgroundColor = "red";
        el.style.fontSize = "30px";
    </script>


</body>

</html>